Electric switch devices



Jan.v 29, 1946. i E, C, WAHLBERG 2,393,846

ELECTRIC SWITCH DEVICES Filed July 1s, 1942 y2 sheets-sheet 1 l//IIIII ATTOR/VE Y 1m29, 194s. E. C. WAHLBERG 21,393,846

ELECTRIC SWITCH DEVICES Filed July 16, 1942 2 Sheets-Sheet 2 uit l I/NVENTOR.

W@ ATTORNEY Patented Jan. 29, i946 UNITED STATES PATENT OFFICE- ELECTRIC SWITCH DEVICES uEric Clifton Wahlberg, Stamford, Conn., assigner to Electrolux Corporation, New York, N.' Y., a corporation of Delaware Application July 16, 1942, Serial No. 451,111

9 Claims.

This 'invention relates to an improved electric switching device, and more particularly to a switch having a plurality of positions and including means for kautomatically retaining the switch in at least one of Ysuch positions 'for a comparatively short though appreciablelength of time.

More specifically, the invention relates to a snap-action switch having two terminal positions and an intermediate position. A switch of this nature includes means for rapidly throwing the switch from one terminal position to the other when a switch handle is actuated. 1n accordance with the'invention, means are provided for automatically interrupting in an intermediate position the throw of the switch which has been initiated by actuating the handle. The switch is held in this intermediate position for a short interval and is then automatically released to continue to travel t the other terminal position without further manipulation by the operator.

vWhile a switch having these general characteristics may find wide application in the electrical art, the particular yswitchherein shown and described is especially suited for controlling in a simple manner the operation of the systemincluding a plurality of electric motors shown and described in applicants copending application Serial No. 428,018 filed January 24,' 1942.

An object of the invention is to provide van improved switch of the above type in whichthe length of time that the switch is held in itsintermediate position may be easily and accurately determined and adjusted.

Another object of the invention is to provide a switch of this type having the switch means removed from the means for stopping the switch in its intermediate position so that the two means will not interfere with one another.

A further object of the invention is to make a switch that is compact in construction and that is easy to manufacture, and that is less likely toget out of order than other switches of the same type.

A further object of the invention is to provide a three pole switch having its contacts so arranged that a misalignment of one set .of its contacts will not cause it to fail to engage one of the other sets of contacts. This is accomplished by means of resilient contacts which are more easily used in a switch of the lconstruction set forth than in other types of three :pole switches. Such an arrangement is particularly desirable when used in the combination set forth for if the switchshould at anytime fail to make 55 proper contact so that one of the circuits was not closed at the proper time, `loss of synchronism of the Vmotors controlled thereby might result.

Another object of thek invention is to provide a three position switch with time delay means for holding the switch in its mid-position when actuated `from one terminal position toward the other in which the time delay will be the same, regardless of the direction in which the switch is actuated.

Still another object of the invention is to provide a three position switch of the type before mentioned in which the time delay means for determiningr the time during which the switch is heldin 'its mid-position is independent of the means for holding the switch in its mid-position so thatV the action of the last mentioned means may -be quick and positive and so that this means may be'made compact and of small size.

A further object of the invention is to arrange the'spring of a snap-action switch of the type mentioned so that the action of the snap-action spring does not tend to cause the switch elements to become misalig-ned when the switch is stopped intermediate its lterminal positions.

A still further object of the invention is to provide in-a switch of the type mentioned a thermal relayfor` determining the time during which Vthe switch is held in mid-position.

Another object of the invention is to provide sucha lswitch which may satisfactorily be used in aircraft. To lthisend, it is an object of the invention to provide such a switch that will operate vsatisfactorily regardless of the position in which it is held. To vthe same end, it is another object t0 provide a switch of this type, using a thermal relay that shall-bke unaffected by changes in ambient ytemperature such as may be experienced if the .device is near the motor of the aircraft or if the aircraftis adapted to fly at high altitudes at which the temperature may be low.

Further objects and advantages of the .invention will be apparent .from the following description considered in connection with the accompanying drawings, which form a part of this specification and in which:

Fig. 1 is a side elevation showing a switching device in accordance -with the invention;

Fig. 2 is a vertical section on an enlarged scale through the device shown in Fig. 1;

Fig. r3 is a horizontal section taken on the line 3 3v `of Fig. 2;

Fig. 4 isa view on astill larger scale of a section taken onf-the line 4-4 of Fig. 2;

Fig.f5 isa rView on .a .somewhat .smaller scale of a section taken on the line 5-5 of Fig. 4;

Fig. 6 is a plan View of a portion of the device shown in Fig. 4;

Fig. '1 is a section taken on the line 1-1 of Fig. 4;

Fig. 8 is a view similar to Fig. 5 showing a modified form of a portion of the device;

Fig. 9 is a section taken on the line 9 9 of Fig. 8; and

Fig. l is a wiring diagram illustrating the manner of connecting a switch in accordance with the invention, in an electrical system of the type described in applicants above-mentioned copending application.

Referring to Figs. l and 2, the switching device comprises a manually operated switch designated generally by the reference numeral I, a thermal relay designated by the reference numeral 2, and an electromagnet designated by the reference niuneral 3.

Referring now to Figs. 2 and 3, the manually operated switch is seen to comprise a switch arm 4 composed of some non-conducting material which is pivotally mounted at 5. A spring 5 connects the switch arm 4 with an operating lever 1 which is also pivoted at 5. Through the switch arm pass rods 8, 9, and I0 adapted to connect the switch contacts on opposite sides of the switch when the switch is moved to one of its closed positions. In the position shown in Fig. 2, the switch arm 4 is in a position in which the members 8, 9, and I9 do not make Contact with any of the xed contacts of the switch and the switch is thus in open position. Fixed at one side of the switch I there are contacts II, I2, I4, I5, and I1. The contacts 8, 9, and I 0 of the switch arm 4 are adapted to engage contacts I4, II, and I1 when the switch is in mid-position and the contacts I5, I2, and I1 when the switch is in its other terminal position. The contact I1 comprises an arcuate strap which is in continuous engagement with the contact I0 when the switch is moved from its mid-position to the other terminal position so that the circuit connected thereto is not broken during motion of the switch from midposition to the second terminal position. On the other side of the switch there are xed contacts I6, I3, and I8, each of which comprises an arcuate strap similar to contact I1 and so located as to make contact with the members 8, 9, ID when the switch arm 4 is in either its mid-position or its second terminal position or any position therebetween.

The contacts Ii through I8 are made of a springy material so that they may be depressed by the moving contacts 8, 9, I0 to a sufiicient extent to provide a good wiping contact therewith. Since the contacts are made of resilient material, even if they should be slightly out of alignment, good contact will be made with all three members 8, 9, and I0.

As best seen in Fig. 2, the spring 6 tends to pull the switch arm 4 and the operating lever 1 together. Movement of the operating lever 1 in either direction about the pivot 5 is limited by means of the stop 9| which engages the casing 92 of the switch. Likewise, movement of the switch arm 4 is limited by engagement of projection 21 with either of the stop abutments 28 or 29. If the operating lever 1 is moved from the position shown in Fig. 2 to its opposite limiting position, the switch arm 4 remains in the position shown until the spring 5 passes over the pivot 5, at which time the switch arm 4 suddenly snaps toward its opposite terminal position. In the switching device shown there is a pin projecting through the casing 92 into the path of the projection 21 on the end of the switch arm 4. rI'his pin 30 stops the switch arm 4 in mid-.position and prevents further movement of the switch arm toward its second terminal position until the pin 39 is withdrawn from engagement with the projection 21. Likewise, when the operating lever 1 is moved back in the other direction towards the position shown in Fig. 2, the pin 30 again arrests the motion of the switch arm 4 in mid-position until the pin 30 is withdrawn.

The pin 39 is actuated by the electro-magnet 3. As shown in Fig. 2, the pin 3|] is mounted on the end of a rod 3| which is in threaded engagement with the armature 32 which is reciprocable within the solenoid 31. The distance that the pin 39 projects from the armature 32 can be adjusted by turning the rod 3| which can be held in adjusted position by means of lock nut 33. The armature 32 is spring-biased outwardly from the solenoid 31 in such a manner as to force the `pin' 30 into a position in which it lies in the path of the projection 21. The exact limit of the inward motion of the pin 30 is determined by the position of the stop nut 35 which is also threaded on the rod 3I. Inward motion of the armature 32 toward the solenoid 31 is limited by means of a stop bolt 36 which is screwed into core 93 of the solenoid 31. When the stop bolt 36 has been adjusted to the desired position, it may be locked in that position by means of nut 95.

As shown in Fig. 2, the thermal relay 2 is mounted on top of the electro-magnet 3. The construction of thermal relay 2 is shown in detail in Figs. 4 through '7. The relay actuates a switch arm 49 to close a circuit between the xed contacts 38 and 39. As seen best in Fig. 5, the switch arm 40 is secured to the base of a U-shaped member having two resilient metal legs 4I and 42 which are xed to the base of the relay casing at 43 and 44. The switch arm 40 is moved between opened and closed position by means of a spring f 45 which in turn is controlled by means of a second U shaped member 46 which is secured to or integral with the ends of resilient legs 4I and 42 beyond the xed points 43 and 44. The ends of the spring 45 are somewhat compressed and tend to push the switch arm 40 as far as possible from the member 46. Thus, if the member 46 is moved up and down in accordance with the position of the bolt 41 connected thereto, the switch arm 40 moves in an opposite direction. Due to the position of the fparts, the expansive force of the spring 45 does not act to move the switch arm 40 until the member 46 has moved slightly past a position of alignment with the legs 4I and 42. For this reason, the switch arm 40 moves from open to closed position with a snap action. The upward movement of the switch arm 40 is limited by means of an adjustable stop 94.

The bolt 41 actuating the member 46 is threaded to an insulating block 46 which is supported by a pair of bi-metallic strips 49 and 50. (See Fig. 6.) The other lends of the bi-metallic strips are attached to a member 5I of some material that is an electric insulator. Pins 52 and 53 serve the dual function of supporting the member 5I on the ears 54 and 60 of terminals 59 and 6I and forming an electrical connection between the bi-metallic strips 49 and 50 and the corresponding ears 54 and G0. The bi-metallic strips are electrically connected together by means of a resistance grid 82 which is connected at one end to the bi-metal 49 bythe pin 63 and at the other .end to bi-metal 50 'by means ofpin 64. A sheet of mica or vother electrical insulator is .placed between the grid 62 and thefbi-metals49 and 5I) to prevent them from short-circuiting one another.

The operation of the above-.described thermal relay is as follows: If electrical power is connected to the ,terminals 59 and 6|, it will flow through the lbi-metals 49 and 59 and the resistance Agrid y52 in series. The heat generated thereby will Vcause the bi-metals to vbend in such a manner as to lift the bolt 41 which in turn lifts the member 46. As soon as the member 46 passes the plane defined by the straps 4I and 42, the spring 45 will with a snap action move the switch arm 40 downward and close the lcircuit between the fixed contacts38 and 39.

InFigs. Band 9 there is shown a modification of the thermal relay illustrated 'in Figs. 4 through '7. The switch member 40 is actuated by member 46 exactly as in the iirst described embodiment. The insulating block 48ais moved up and down by means of bi-metallic strips in exactly the same manner as member 48 in the first embodiment. However, the member 48a is not mounted above the member 46 as in the previously described embodiment but is instead mounted in the same plane therewith. r'Ihe member 48a is connected to the member 46 by means lof la long tongue 1II having a forked end 1|. The member 1I) is preferably made of bimetallic material and the bi-metallic elements thereof are reversed with respect to the position ofthe bi-metallic elements 49 and 50. With this arrangement the position of the fork 1I may be made to be independent of the ambient temperature, for any movement of the member 48a caused by response of bi-metals 4,9 and 50 to changes in ambient temperature will be exactly offset by an opposite movement of the bi-metal 10. Bi-metal 10, however, is thermally as well as electrically insulated from b-metals 49 and 5I) by the member 48a, so that when current is passed through bi-metals 49 and 50 and the grid 92, the thermal relay will operate in the manner of the first-described relay. Since the lever arm provided by ybi-metal 1| increases the magnitude of the movement of member 46 in response to bending of bi-metals 49 and 56, the Athermal relay in this embodiment will be more sensitive than the relay first described.

Referring to Fig. 10, there is shown the scheme of connections between the manually operated switch I, the thermal relay 2, and the electromagnet 3. There is also shown a manner of connecting the entire switching device to a circuit for controlling the operation of synchronously operating direct current motors. It will be understood, however, that the same switching device may be used in other connections. Reference numerals 84 and 85 designate a source of direct current power which is connected by leads I9 and 2| to fixed contacts I8 and I6 of the manual switch I'. A group of direct current motors 8|, 82, and 83 are connected by leads 24, 25, and 26 to the xed contacts I1, I2, and I5 of the manual switch I. When the manual switch is in its second terminal position designated by III, the rsource of power is connected to the brushes of the motors. This circuit may be traced from power terminal 84 through lead 2|, contacts I6 and I5 and lead 26 to one group of brushes, thence through the armatures of the motors and back from the other set of brushes through lead 25 and contacts I2 and II3 to lead 29. Lead 29 is connected to ground .and :likewise :the motor -iields are ,connected atone .side to ground. The `other side -of the motor fields, which are connected `in parallel, is connected :to lead 24. From lead 24 the circuit proceeds through contacts `I1 and I8 and lead I9 back to the other side ofthe power source at terminal 85. 'Ihere is a three phase connection 86 connecting slip rings `|31, .89, `and 89 ofthe motors 8| through 83. The slip lrings are connected to fixed taps taken from the armatures of the motors at intervals of roughly 120 degrees. The three phase connection 86 serves to maintain the motors in synchronism as more fully set forth -in my above-mentioned copending application. Two of the leads forming the three phase tie between the motors `are also connected'by means of leads 22 and 23 to iixed contacts II and .I4 `of the manual switch I. When the manual switch is in its mid-position .designated by II and IV, the source .ef kelectric power energizes the fields of the motors as before in position III from terminal through lead I9, contacts I8 yand I1 and lead 24 through the fields to ground. The brushes of the motors are not connected, however, and instead the ground lead 20 connects the source of power through y.contacts I3 and II to lead 22 and thence through one set of slip rings and va portion of the armature of each of the motors andout through another set of slip ringsback to lead 23, contacts I4 and I6, lead 2| to terminal B4 at the rother side lof the direct current source of.power. As set forth in my copending application, this connection of the motors serves to cause theirarmatures to assume definite positions of alignment Vwith respect to their fields.

When the switch is in position II, IV, the thermal relay 2 is also energized from the direct current source of power. This circuit may be traced from terminal 94 through lead 2|, contacts I6 and I4, lead 23, lead 55, bi-metal 49, grid 62, bi-metal 50, lead 58, lead 22, contacts II and I3, and thence from lead 20 through ground to the field circuits and back through lead 24 through contacts I1 and I8 and lead I9 to terminal 85. Thus, whenthe switch I is moved from its open position corresponding to I to the mid-position II, the synchronous motors are first brought into alignment. Then after a definite time, depending upon the constants of the circuits, thermalrelay 2 is actuatedto close its contacts 39 and 38 through switch member 40. This causes energization of electro-magnet 3 in parallel with thermal relay 2 from the leads 22 and 23. When electro-magnet 43 is energized, its armature moves inwardly towar'ds its solenoid, retracting pin 3U and allowing switch arm 4 of manual switch I to move to its second terminal position designated by III. The motors then start up and operate synchronously as long yas the manual switch is left in this position.

When the manual switch is in position III, the thermal relay 2 and the electro-magnet .3 are both ie-energized so `that the armature 32 of electro-magnet 3 is forced outwardly from solenoid 31 by spring 34, thus projecting pin 30 into the path of the projection 31 on the end of switchfarm 4 of the manualswitch I.

When it is desired to stop the motors, the operating lever 1 of the manual switch I is moved into its opposite position which tends to move switch arm 4 to its open position. However, the pin 30 holds the switch arm 4 inmid-position designatedin Fig. 1,0fby IV. lIn this position the brushes ,fof .the motors vrare ,disconnected from the power source and direct current is applied to two taps on the armature of each motor through a pair of slip rings as in position II. This application of direct current to fixed taps on the armature of each of the motors causes them to be quickly brought to a stop. Since the motors are still connected by means of the three phase conneotion 86, they decelerate in synchronism. When the motors finally come to rest, they are all brought into alignment with one another as described before when the switch was moved from position I to position II.

While the motors are decelerating and coming to rest, the thermal relay 2 is again energized and after a definite time closes the circuit through the electro-magnet 3 which, as above described, withdraws pin 3D from the path of projection 2l on the switch arm 4 and allows it to snap into its open position as shown in Fig. 2.

If it is desired to change the length of time during which the manual switch is held in midposition, this can easily be accomplished by Varying the position of bolt 4l in member 48 of the thermal relay 2. The thermal relay may also be adjusted by adjusting the position of stop 94. If a variable resistance is inserted in series with the actuating elements of the relay as at 9B, the time delay of the relay 'may be adjusted electrically. It is to be noted that time delay between energization of the thermal relay and the closing of its contacts is independent of the direction of movement of the manual switch into its mid-position.

Since a separate relay has been used to determine the time during which the manual switch is held in its mid-position, the electro-magnet actuating the stop pin 39 may be made quick acting and compact and its operation can be made to be independent of its position. Because the spring 34 exerts a greater force than the weight of the armature 32, the armature will not move except under the action of the solenoid even when the electro-magnet is turned so that the weight of the armature tends to move it inwardly. Likewise, the solenoid is made strong enough to draw in the armature even though the electro-magnet is in such a position that the weight of the armature is added to the bias of the spring 34 tending to force the armature outwardly.

Since the time delay mechanism is of the thermal type rather than the mechanical dashpot type, the time delay is also independent of the position of the switching device. The moving elements of the thermal relay are all of light weight compared with the actuating forces of the spring and the bi-metals.

The manual switch itself, being always springbiased toward one position or the other by a spring having a forcelarge compared with the weights of the moving parts of the switch, is also independent of position as far as its operation is concerned.

Since the spring of the snap action manual switch is always in tension, it holds the moving elements together even though the switch is arrested in mid-position. This is an advantage over known switches of this type in which the spring was in compression, serving to bias the switch arm against the xed contacts as well as to move the switch. With the previous form of switch, the parts were apt to become cocked at an angle when arrested in mid-position.

Since the contacts of the manual switch are mounted on either side thereof, the end of the switch arm is left free for cooperation with the stop pin. Oi! course the position of the stop pin and contacts could be interchanged, the important thing being to separate them so as not to interfere with one another.

It will thus be seen that there is provided by the invention a switching device fullling all of the objects set forth at the beginning of the specification. While two preferred embodiments of the invention have been described, it is obvious that many modifications therein might be made by one skilled in the art and it is intended to cover by these Letters Patent all forms of the invention falling within the spirit and scope of the appended claims.

I claim:

l. A pivoted switch arm, a plurality of conducting members supported on said arm at right angles to the plane of movement thereof and spaced radially from one another, stop means for limiting rotation of the switch between two end positions, a spring biasing the switch arm into the nearest end position, an abutment on the end of the switch arm, stop means spring-biased into a position projecting into the path of the switch arm at a point midway between the end positions where it will engage said abutment when the switch arm is actuated from one end position toward another to prevent further movement to said other end position, and means for withdrawing said stop means.

2. A switching device comprising a manual switch having a switch arm rotatable between two extreme positions, an electro-magnet mounted on the manual switch having a solenoid lying in the plane of movement of said switch arm and having an armature movable along an axis passing through the center oi rotation of said switch arm, a projection on the end of the armature lying in the path of the switch arm when the armature is in extended position, means to bias the armature to its extended position, and time delay means set in operation by the manual switch when held in mid-position by said projection for energizing said solenoid after an appreciable time, said solenoid when energized being adapted to overcome said biasing means and retract the armature to such an extent that the projection no longer lies in the path of the switch arm.

3. A three position switch including a switch arm having two terminal positions and a midposition, manual means for initiating movement of the arm from one terminal position toward another, means for arresting the switch in midposition, thermal means energized when the switch is in mid-position for releasing said arresting means after the switch has been in said mid-position a deiinite period of time, said period being the same regardless of the direction from which said switch reaches the mid-position, and means for continuing said movement of the arm to said other position after release of the arresting means.

4. A three position switch, means for moving the switch from an end position to a middle position, means tending to cause the switch when in a middle position to move to an end position opposite to that which it last occupied, means for preventing Amovement of the switch past the middle position until a denite time after it has been moved from an end position, and thermal means set into operation when the switch is in a mid-position for releasing said movement preventingi means.

5. A synchronous motor controller comprising a three position switch including a switch arm having two terminal positions and a mid-position, means for initiating movement of said arm from one terminal position towards the other terminal position, relay means controlling a lock for interrupting said movement of switcharm and temporarily holding the latter in its mid-position,

thermal means controlling the time during which the switch is locked in mid-position, temperature responsive means for compensating said thermal means for changes in ambient temperature so as to maintain constant the period of time during which the switch is locked in mid-position, and means for continuing said movement'to said other position upon release of said lock.

6. A motor controller adapted for use on aircraft comprising a manual snap action switch having a spring for producing the snap action, an electro-magnet actuating a. lock for holding the switch in a position midway between its end positions, said electro-magnet having a solenoid and an armature therefor and a spring biasing the armature outwardly from the solenoid into switch locking position, said snap action spring and said biasing spring and said solenoid being strong enough compared to the weight of the parts actuated thereby to perform their functions in their normal manner regardless of the position of the controller relative to the earth.

7. A three position switch, means for moving the switch from an end position to a middle position, means tending to cause the switch when in a middle position to move to an end position opposite to that which it last occupied, means for preventing movement of the switch past the middle position until a definite time after it has been moved from an end position, thermal means set into operation when the switch is in a mid-position for releasing said movement preventing means, said thermal means comprising a bimetallic strip which is heated by electric current when the switch is in the middle position.

8. A three position switch, means for moving the switch from an end position to a middle position, means tending' to cause the switch when in a middle position to move to an end position opposite to that which it last occupied, means for preventing movement of the switch past the imiddle position until a denite time after it has been moved from an end position, thermal means set into operation when the switch is in a midposition for releasing said movement preventing means, said thermal means comprising a bimetallic strip which is heated by electric current when the switch is in the middle position and a second bimetallic strip connected to the rst bimetallic strip but thermally insulated therefrom and mounted with its component metal parts reversed with respect to said first bimetallic strip.

9. A three position switch having an open circuit position, a conditioning circuit position, and a closed circuit position, snap action means for moving said switch between open and closed circuit position, spring means for holding the switch in conditioning position for a predetermined time whenever the switch is moved between open and closed positions, magnetic means for overpowering said spring means, thermo-electric means for setting into action said magnetic means, and switch contacts closed by said switch in its conditioning position completing a circuit to said thermo-electric means.

ERIC CLIFTON WAHLBERG. 

